title: Discriminative validity of metabolic and workload measurements for identifying people with chronic fatigue syndrome.
abstract: BACKGROUND
  Reduced functional capacity and postexertion fatigue after physical activity are hallmark symptoms of chronic fatigue syndrome (CFS) and may even qualify for biomarker status. That these symptoms are often delayed may explain the equivocal results for clinical cardiopulmonary exercise testing in people with CFS. Test reproducibility in people who are healthy is well documented. Test reproducibility may not be achievable in people with CFS because of delayed symptoms.
  
  
  OBJECTIVE
  The objective of this study was to determine the discriminative validity of objective measurements obtained during cardiopulmonary exercise testing to distinguish participants with CFS from participants who did not have a disability but were sedentary.
  
  
  METHODS
  A prospective cohort study was conducted.
  
  
  METHODS
  Gas exchange data, workloads, and related physiological parameters were compared in 51 participants with CFS and 10 control participants, all women, for 2 maximal exercise tests separated by 24 hours.
  
  
  RESULTS
  Multivariate analysis showed no significant differences between control participants and participants with CFS for test 1. However, for test 2, participants with CFS achieved significantly lower values for oxygen consumption and workload at peak exercise and at the ventilatory or anaerobic threshold. Follow-up classification analysis differentiated between groups with an overall accuracy of 95.1%.
  
  
  CONCLUSIONS
  Only individuals with CFS who were able to undergo exercise testing were included in this study. Individuals who were unable to meet the criteria for maximal effort during both tests, were unable to complete the 2-day protocol, or displayed overt cardiovascular abnormalities were excluded from the analysis.
  
  
  CONCLUSIONS
  The lack of any significant differences between groups for the first exercise test would appear to support a deconditioning hypothesis for CFS symptoms. However, the results from the second test indicated the presence of CFS-related postexertion fatigue. It might be concluded that a single exercise test is insufficient to reliably demonstrate functional impairment in people with CFS. A second test might be necessary to document the atypical recovery response and protracted fatigue possibly unique to CFS, which can severely limit productivity in the home and workplace.
authors.affiliation: C.R. Snell, PhD, Department of Sport Sciences, University of the Pacific, Stockton, California, and Workwell Foundation, Ripon, California.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Snell
authors.forename: Staci R
authors.initials: SR
authors.lastname: Stevens
authors.forename: Todd E
authors.initials: TE
authors.lastname: Davenport
authors.forename: J Mark
authors.initials: JM
authors.lastname: Van Ness
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D015673:Fatigue Syndrome, Chronic / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D010101:Oxygen Consumption; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D015203:Reproducibility of Results; D057185:Sedentary Behavior